Honolulu resident Deborah Tamura first noticed the sick and dying ducks during her early morning walks through Kapiolani Park this summer.

She saw sickly-looking ones as early as July, first near Iolani stream and then at the man-made ponds near Kapiolani Park Bandstand in Waikiki. As an animal lover, it was devastating to find the dead ducks, particular ones she had nicknamed after seeing them regularly.

“I’m extremely sensitive, so it’s hard,” she said.

Over the past two months, Tamura said she and a friend turned over about 50 sick and dead ducks, mostly to the Hawaiian Humane Society but also to local veterinarians. About half were sick and half were dead, she said. She had no idea what was making them sick.

Dr. Eric Ako, a veterinarian with a special interest in avian medicine, thinks botulism was the likely cause of the ducks’ illnesses. The symptoms include weakness, lethargy and not fleeing when approached by a human.

Botulism is a natural toxin produced by a bacterium, Clostridium botulinum, and birds can get sick from swimming around and drinking affected waters. Typically, it happens in stagnant water. It can happen when pumps are not working properly.

“A few weeks ago it was super hot and humid,” said Ako. “I suspect that was the trigger, the weather.”

Botulism is not contagious from duck to duck, said Ako. However, a pet dog that went into affected waters or ate or mauled one of the dead ducks with botulism can potentially ingest the toxin and die, as well.

The Hawaiian Humane Society confirmed receiving more than a dozen deceased or very ill ducks. The very ill ducks were euthanized, a Society spokesman said.

On Aug. 22 Tamura again picked up two sick ducks and one dead duck at the park.

One of them, a young mallard she had nicknamed Sunny Skies, looked like it could still recover, so she took it to Feather &Fur Animal Hospital in Kailua. A private nonprofit, the Hoof Talon and Paw Foundation, stepped in to foot the bill.

Sunny Skies recovered with supportive treatment and was released back into the wild.

Dr. Brian Walsh, medical director at Feather and Fur, said the animal clinic has been receiving some of the ducks and was able to treat two successfully and release them.

He also thinks the likely cause of their illnesses was botulism. But usually, botulism occurs in muddy, swampy bodies of water.

“I couldn’t say 100% what’s going on, but that’s the most common cause of duck die-offs,” he said.

In the past the clinic has treated native birds suffering from botulism, including Hawaiian moorhens and coots. There have been occasional outbreaks, but it is unusual for such a large number to be affected at one time, he said.

The staff at Kapiolani Park also observed sick ducks in and around the bandstand ponds Aug. 22, according to city Department of Parks and Recreation spokesman Nathan Serota.

“There is no indication that the conditions in the ponds led to these injured and deceased ducks,” said Serota in an email. “The ponds are cleaned daily, whether that involves removal of debris, cleaning the filters, or chlorine treatment (similar to pools).”

Serota said the incidents have been referred to the state Department of Land and Natural Resources’ Division of Forestry and Wildlife.

State DLNR spokesman Dan Dennison said since the ducks are feral mallards, they are not a DOFAW priority species. If it is a botulism outbreak, DOFAW can provide technical expertise, he said.

“Since the area of concern is not near any State Wildlife Sanctuary or priority native species habitat, we would defer to the responsible landowner or agency to implement mitigative protocols,” Dennison said in an email. “Mitigation will require on the ground resources and constant monitoring.”

Both the city and state reminded the public not to feed the wild ducks.

The situation seems to have improved for now, according to Tamura. Last Wednesday she noticed waters around the Kapiolani Park ponds were cleaner. Several ducks, including a pair of baby ducks, were splashing around contentedly.

She is hoping her encounters with dead ducks are behind her for now.

Without doing a necropsy and some tests on the dead ducks, Ako said it is difficult to know for sure what was ailing the ducks. Based on the symptoms these ducks were exhibiting, they likely suffered from botulism.

It would not be the first time ducks have succumbed to botulism outbreaks in the islands.

According to the U.S. Geological Survey, avian botulism can occur year-round. It has been found on Kauai, Oahu, Molokai, Maui and Hawaii. Recent outbreaks of botulism have even occurred at Midway Atoll in the Northwestern Hawaiian Islands, affecting critically endangered Laysan ducks.

More than five years ago, Ako said, there was a healthy duck population at the end of Hawaii Kai Drive, but those birds are mostly gone now. Ako said they died from a documented case of botulism.

Other waterways where ducks potentially could be affected around Oahu, he said, include Paiko Lagoon, Enchanted Lake and Hamakua Marsh in Kailua, Salt Lake and Pearl Harbor. Property managers who oversee man-made ponds should be aware of possible outbreaks.

“It tends to be when it gets super hot and doesn’t rain, when water flow is inadequate,” he said, “so it would be incumbent upon caretakers to recognize what’s happening with the weather and turn the pumps on.”